Recovery of sulphuric acid from acid sludge



Qct. 23, 1945. J. "G, LILI ARD ETA; 2,387,519

RECOVERY 0F SULPHURIC CID FROM ACID `SLUDGE Filed July 22. 1942 o Patented oei. 2a 1945 I s PATENT OFFICE- .f UNITED STATE i normally gaseous hydrocarbons. i i In the refining of heavy lubricating cil stocks,

. y micovnmz OFSULPHURIC AolnFRoM ACID SLUDGE Oil Development Company, a corporation of Delaware Application July 22, 1942, Serial No. 451,&72

s claims. `(o1. 23-173) 'Iehis invention relates to an improved procedure for the recovery of sulphuric acid from sludge materials obtained in the refining ofmineral oils with concentrated sulphuric acid'. More `particularly the invention isA concerned with the recovery of sulphuric acid from sludges resulting i. from the sulphuric acid treatment of residual crude petroleum fractions 'dissolved in liquefied a recent development has been to effect the treatmefnt `with sulphuric acid 4in the presence of a pane acts simultaneously as a diluent and as a n distinct treating agent. `The acid sludge derived from such treating is therefore -of a different character from that normally obtained from acid treatingresidua in the presence of an inert diluent,such as treated naphtha.4 stock. Due to emulsion troubles; acid sludges derived fromy such sulopment of emulsions.

phuric `acid treatments of residual lubricating oil stocks,tparticularly from Mid-Continent or parallnlc typefcrudes, are diilicult to decompose and -resolve into theiroily constituents and acid constituents' by the usual hydrolysis method. In `this procedure the acidsludge is'agitated with water` or water and a light `petroleum stock. The

emulsication dimculties have been largely overcorne by the use of demulsiiying agents and by `dissolving the acid sludge iirst in a-solvent, such theA sludge which permits the material to be hydrolyzed more easily. lThus, the treatment of acid sludges with hydrocarbon distillates of the naphtha, kerosene and gas oil ranges enables the sludge material to be relatively easily hydrolyzed by either water or dilute acid without the devel- This hydrocarbon treatment of the sludge material isa means for olotaining higher yields and better concentrations of acid than hithertofore obtainable by prior art procedures. Furthermore, the acid recovered by the method of this invention is cleaner 'than that obtained from current conventional methods and, therefore, does not fouleequipment used in concentrating it to higher strengths.- A

The preliminary treatment with a light petroleuxn oil of acid sludges derived from4 the sulphuri acid treatment of residum lube stocks and the separation of the oil fromthe sludge prior to the hydrolysis of the sludges accomplishes two desirable eilects: First, the sludge material is rendered more amenable to acid recovery and, sec-- oil as the agent for conditioning the sludge for.

as an aromatic'distillateyand vthen hydrolyzing the; mixture. i Such procedures ffor treating acid sludges `are not wholly satisfactory from the viewpoint oinyilds and. furthermorethey are rela- Q `tively expensive because ofthe costs -involvedin theuses of the demulsifying agent and the solvent. p The present invention. is an improvement over theprior art procedures in that an effectiver and inexpensive means is provided forrecovering acid in higher yields andin higherconcentrations froin acid sludges derived from the sulphuric 4acid treatment `oi' residuum lubricating oil stocks `inthe presenceof a e o liqueed normally gaseous hydrocarbon. H

'I'he invention is concerned with a treating procedure to which the sludge material is subjected priorto the hydrolysis step. It has been `found` that, if the sludge material after separation from the oil phase from which it is derived is intimately contacted with a proportionately large volumeof the hydrolysis treatment. It has"n been found for example that in some cases the residuum acid sludges impart both acid treating and sweetening effects (similar to doctor treating) upon such raw petroleum oils as cracked naphtha, kerosene or gas oil, when such stocks are employed in accord' ance with the procedure of this invention. -These treating effects,`especially that of s'weetening, are

obtained as being distinctly additive to that of the commonly recognized residual acid effects o1- most sludge compositions'. Furthermore, these effects are obtained in addition to that of favorably conditioningI the sludge material for 'subsequent hydrolysis to ywhich many acid sludges do I not respond advantageously. Thus, it has been 1 found that the acid sludge derived from the sul- `s: light petroleum oil distillate, preferably a raw s "o1" untreated distillate having a gravity between 2SA. P. I. and 55-A. P.I., an effect occurs upon 55 e In accordance with this invention 'acid sludges phuric acid treatment oflight and medium Panhandle lubricating loilv distillates in the presence of liquefied propane cannot be satisfactorily" co`n ditioned for hydrolysis by treating with raw kerosene distillate in'accordance with they procedure` of this invention.A On the other hand, the acid sludge obtained/from thesulphuric acid treatment in propane solution of Panhandle residuum heavy lubricating oil stock does respond readilyto thi sludge conditioning treatment.

mixed in mixing device obtained from the sulphuric acid treatmentof petroleum residuum lubricating oil stocksV in a liquefied normally gaseous saturated hydrocarbon, such as cth-ane, propane, butane or pentane, are thoroughly mixed with a light petroleum` oil distillate; such as cracked naphtha-kerosene orl mixture separates ninto a predominantly o il phase gas oil, and then the mixture is allowed to settle and separate intoan acid phase and an oil phase.` The acid phase comprises the conditioned'sludge Awhich is readily hydrolyzed by agitatingiit with lwater or dilute acid. Thus, the conditioned sludge is decomposed by hydrolysis into dilute acidand an oily material which may be`l used as-a fuel or for. other purposes if desired. 'The oil phase vseparated from the sludge during the conditioning vtreatment contains, as a rule, a considerable por'- tion of the acid material originally present in the sludge. This acid or acid material acquired by the .treating oil appears t'o be primarily in solution orl in colloidal suspension as only a small amount of it can beremoved by lteringj the oil through paper. This acid material is best removed from the treating oil by hydrolysis which y conditions in order to avoid emulsion vdifllctllties. lThe emulsion difculties are avoided by ru'eheating the oil to a temperature in the range between about 170 F. and 210 F. before it is contacted with steam and/or hot water to eiect hydrolysis vof the acid material contained therein. The hy-V' into a. dilute acid phase and a hydrocarbon phase. The hydrocarbon phase may be neutralized and then distilled to recover a light oil of marketable quality except for belnglvery slightly so'ur to the doctor test anda hydrolyzed oil suitable for use vin fueloils.

The process" of .this 'invention may be better ment. For purpose of description it is assumed that the acid sludge is a sludge obtained in the sulphuric acid. treatmentfin propane solution,

.understood by reference tothe attached draw-- ing which is a ilow sheet of a preferred embodiand a predominantly sludge phase. The oil phase comprises treated kerosene together with 'a considerable portion of the acid material originally present in the sludge. This acid material is p rimarily inthe form of a solution or colloidal sus# r- 4pension in the oil and cannot be readily separated byl mechanical means.

Thesludge phase separating in settler 5, comprising the so-called fconditioned sludge, is withdrawn through line i and' passed to stripping l still 1. Still 1 is supplied with.suitable connecmust be carriedv out under carefully controlled tions for heating and for pressure reduction so v that low boiling materials, such as propane, and sulphur dioxide may be distilled overhead through line 8. The sludge thenpasses through line 9 and is intimately mixed in mixer-hydrolyzer I0 with dilutesulphurc vacid supplied through line. Il. Although l.itis preferable .to employ dilute sulphuric acid ot about% strength as the hydro. lyZing agent, water may be'introduced through line l2 land employed either alone or in supplement to dilute acid to eiect hydrolysis of the sludge. In this manner, rapid `and complete' hyydrolysis'of the sludge is effected, and it usually voccurs without heating except as supplied by the l reaction. However, in some cases it may be dedrolyzed mixture is then. settled and separated sirable toemploy steam as a ingmedium.

vThe hydrolyzed mixtureis passed from mixerhydrolyzer In through line' l? to settler i4 wherein phase sepa-ration occurs betweena substan- .tially aqueous acid vphase -Y and anch-insoluble carbonaceous phase. Y'I'he oil-insoluble carbona-y ceous phase is removed from settler I4 by means of line l5 or the equivalent thereof and it `may f be employed as a low-grade fuel or itmay be otherwise disposed of as desired. The acid lphase i t' s is removed from settler H by means oi' line i6. 40'

ois. heavy residual lubricatingoil stock. It is4 further assumed that the light petroleum; oil employed as `a treating agent in the conditioning of the sludge for hydrolysis is a raw or untreated kerosene distillate.

. By means of line` I,l a stream of untreated kerosene distillate is introduced into a stream or propane-containing residuum acid sludge flowing through .line 2 and the combined streams areintroduced into mixer 3 for intimate mixing'y pref ly at normal temperatures. For the purpose of this illustration, the amount ot kerosene-mixed with the sludge material is about seven 'times for sludges obtained fromA the acid treatment in propane solution. of heavy residuum lubricatingl oil stocks.y j

The oil sludge mixture, after being. intimatelyv 3, is then discharged through lined to 'a settler 5. lIn settler- ,5 the conditions are suitable for satisfactory phase-serif 'I'he strength of thisaci'd phase depends upon the proportion'of water or dilute acid used to the quantity of acid present inthe sludge hydrolyzed therewith. It is preferable to employ the-mini-v mum amount of water or dilute acid which is,

conducive to good operation in effecting the hydrolysis of the acid sludge in orderto avoid un necessary dilution o! thefacid phase which is subsequently concentrated to produce strong acid.

Usually the acid obtained through line I6 hasv a concentration of about 50% HzSOo.-

Theoil phase comprising treated kerosene I gether with some acid material, as separated in settler 5, is withdrawn from settler 5 by means of line Il and it is passed through heater "wherein it is preheated .to .a temperature above about 155A F.; preferably between about 170 F. and 310 F.,

before being passed through line I! to hydrolyzer 20. `In hydrolyzei' 2|. the oil is treated with steam n or hot water to effect hydrolysis o! the acid mate#- eration; that is, the rate of flow therethrough and the form of the equipment are ladjusted to give 's desirable settling time.m Although not critical, a settling period of about one hour is usually required.` During thissettling 'period the oilsludge iii` rial contained therein.- The'hydrolysls treatment is preferable to other methods oi' decomposing and removing acid materials from the oil since it permits recovery of the sulphuric acid involved therein. However, itis necessary that the oil be preheated to and maintained at atemperaturein the range .between about F. and 310 F. durf ing the hydrolysis treatment with steam or hot water, introduced by means of line 1I, 'in order I to avoid emulsion 'diliicultieal Contact between the oil and the hydrolyzing agent in hydrolyzer 20 is maintained for a timesulllcient to eiect complete-hydrolysis of the acid materials present i in the oil, as wellas the removal or low boiling materialasuch as propane, betorethe mixture is discharged through line nto settler 23. A con v heating and agitat-- i forthis purpose. The low-boiling, materials are removed by means of line 24; "11n settler 23; the conditions are suitably ad- Vjusted to: permit satisfactory phase separation within a reasonable. operation period, such as through line 25, is comprised of treated kerosene about an hour. Thus, the hydrolyzed mixture is separated `into-e. dilute acid phase and a treated f oiliphase. The treatedoil phase, withdrawn togetherjwith` some dark, oily hydrolysis prod-`V` test.

ucts;` hence, it preferably is neutralized and re- `fdistilled to produce` a kerosene of good quality except for being `very slightly sour to the doctor The dilute acid obtainedin settler 23 is withdrawn through line26 and may-be further proc- `essedto obtain a solution of higher concentration.

The strength of this dilute acid may vary over a considerable'rangedepending upon the quanandseparate into an noil phase and a phase of newly formed or "conditionedf sludge. The conditioned' sludge was hydrolyzed by agitating it with water. In the following table the results are presented:

Conven- Present .sa am Raw sludge .pounds.. 100 100 Oil fraction added do 161 565 Demulsifying agent added do.--. 24.5 Water added -d0-... .66.8 28.

Acid in demulslfying agentdo.. 3. 7 Total acid (sludge plus demulsifyin agent),` pounds of equivalent 100 o v H2504 42.4 34.4 Acid recovered, pounds of equivalent 35.2 32.3 100% HiSO Percent total acid recovered v 83. 0 94. 0 Carbonia acid per cent' by weight-. 3. 4 1.0

tity of steam or hot water employed in the hy'- l drolysis in proportion vto the amount of acid materialpresent in the oil being subjected tothe hydrolysis treatment. Usually the proportions of ,these materials are adjusted to'obtain a dilute acid of about 30% H2SO4 strength.

`It isfound advantageous in many cases to refcycle and employ a portion of the acid obtained i in settler 23 as a means, of preheating all or a Yportion of the oil (containing the acid material) which is `withdrawn from settler 5 -by means of line Il.` f The recycleddilute `acid also serves as an aid` tothe` steam or hot water in effecting hy- In operations 'of this nature, dilute acid is passed from settler 23 through lines eand 21 to line 2'8 wherein it is admixed with oil diverted from line I1. This mixture of oil and dilute acid is then passedthrough incorporator 29 for intimatemixing before being discharged through line 30 t'o hydrolyzerZ. Lttleor no emulsiondiiliculties to employ the dilute acid obtained in settler 23 as aineans for hydrolyzing the .acid sludge charged to mixer-*hydrolyzer I0. In this mode of operation, a portion ofthe acid is passed from.

settler 231through lines 26 and 21 to line `Il from whence it flows to mixer-hydrolyzer i0 in the manner hereinbefoe described.

i l drolysis ofthesl'udge material present in the oil.

Hydrolysis 'of conditioned sludge Type of hydrolysis l Aqueous Dilute acid Hydrolysis temperature, "F 180 185 -Hydrolyzing agent added, wt. percent of sludge. v, 06.6 124 cid recovery, wt. percent of charged materlals 81.4 80.8 StrengthV of recovered acid, wt. percent 1 35.1 49. s Acid recovery from conditioned sludge, wt. rcent based en unhydrolyzed con itioned" sludge 96.6

As a further means of understanding this inj `vention,tl'ie following examples are presented:

Example I of a sludge material obtained 'Two portions Wfrom thesulphuricacid treatment of a Panhandleheavyresiduum` lubricating oil stock while dissolved in propane were treated for acid recovery i by (l) what is commonly considered the conven- The conditioned sludge, resulting from the treatment of the initial sludge material with the 43 A. P. I. gravity oil fraction of Example 1, wa-sA divided into two portions. One portionl was hydrolyzed by adding water and the other lportioii was hydrolyzed by adding an equal volume of dilute sulphuric acid separated from settler 23 as previously described. The acid used for hydrolysis analyzed 31.3% sulphuric acid. In the following table the data are presented:

i These data indicatel that, in order'to recover an acid of high concentration, it is preferable to employ dilute acid rather than water as the hydrolyzing agent.

In the prior art the advantage of employing hydrocarbons to eiiect'a pre-treatment of sludge Vmaterial in order to render the sludge more tionalmethod and" (2) the process according to this invention. In the first or conventional case `the sludge was uxed with an oilhaving a 398 li.` *initialboiling point, a 664 ilnal .boiling point and a 31.5"` ALP. 'I. gravity'.V This mixture was subjected to hydrolysis treatmentgwith water v v*underagitating conditions which resulted in the formation of an emulsion. The hydrolyzed mixamenable for acid recovery was not appreciated. The eect of the hydrocarbons inQhis capacity is not understood. The effect is not that of a iluxing medium, since in many cases a particu-` larly desirable treating effect is imparted to the hydrocarbons by the sludge and the hydrocarbon "is present in the sludge during the subsequent hydrolysis treatment in only very small amounts. The ellect of the hydrocarbons upon the sludge is, furthermore', believed wholly unexpected from Y Drior-artprocedures for the recoveryof acid ture was Athen treated with a demulsifying agent to resolve the emulsion `and effect separation of a dilute acid phase and an oil phase. In the sec-i i ondcase, a distillate having a 357 F. initial boiling point, 'a 529 F. final boiling point and a 43 A. P I. gravity was mixed and agitated with the sludgeiflflhe mixture was then allowed to settle from sludge materials.

Numerous advantages also follow from the use of the procedure of the present invention for the recovery of acid from acid sludges obtained in the sulphuric acid treatment of petroleum residuums while dissolved in liquefied normally gas.-

eous hydrocarbons. The method is particularly applicable in the recovery of acid from the highthe formatio carbon may be similarly employed -a temperature otbetween about 155 vr'. to` effect .the hydrolysis of the acid material the acid treatment of Mid-'Continent type residuum lube stocks whilev dissolved in liquefied propane. The sludge materials obtained from such proc' esses have in the past presented considerable ditilculty in rennery acid recoveryi processing. The higher yields of acid obtained and the= lower car-a bon content ofthe acids so obtained are also important advantages of processing according to the presentinvention. These latter advantages are-moreover. obtained as a result of obviating many of the deteriorating reactions which have occurred in m ny prior art procedures involving of` substantial phuric acid'materials.

. While the procedure of the invention has been illustrated in connectionwith the use of a petroleum fraction boiling inthe kerosene range with vsludge obtained from the sulphuric acid .treatment, in propane solution, oi' a Panhandle resid, uum heavyllubricating oil stock. other `petroleum fractions within-the gravity range vof 25 to 55 A. P. I. such as naphtha, gas oil and heating oil, and other sulphuric acid sludges derived from the acid treatment of a petroleum residuum while quantities of sul-l 2. 'Ihe improvement according to claim l in v, which the sludgematerial is obtained from the treatment with concentrated sulphuric acid with t dissolved in a liqu'eed normally gaseous hydroin refinery processing.

What is 'claimed is:

1. In the recovery of sulphurlc acid by the the sludge material lseparated from theV treatedto advantage b petroleum residuum oil dissolved in the liquefied 1 normall gaseous saturatedl hydrocarbon withV a petroleum oil having a gravity of between about 25 and. 55 API, settling, causing a'. predominant- -iled propane.

a petroleum residuum oil while dissolved in lique- 3. The improvement according to claim 14 in which the petroleum oil having a' gravity ot'between/25 and 55 API is kerosene.

4. The.improvement according to claim 1 in iwhich the treating ot the 'predominantly oil phase with water is eiiected at a. temperature of between about 170 F. and 210 F. i

5; An improved process for the recovery of sulphuric acid from sludge material obtained in the treatment with concentrated sulphuric acid of a petroleum vresiduum o'il dissolved in a llqueed l normally gaseous saturated hydrocarbon, which comprises agitating the sludge -:materialseparated from the treated petroleum reslduum oil disf solved in the liquened normally gaseous saturated hydrocarbon with a petroleum oil having a gravity o! ybetween about-25 and 55 API, settling, causing a ypredominantly sludge phaseto sepa' rate from a predominantly oil phase, treating the said predominantly oil phase with iwater at .a

4temperature of between about-1509K and 210 F. to effect the hydrolysis of the acid material lysludge 'phase to'separate from a predominantly oil phase, treating said oil phase with water at'` F. `and 210 nantly aqueous phase'- to the said predominantly sludge .phase 'to leilect hydrolysis thereof.-

phase withwa'ter is effected. at a temperature --dominantlyoil phase and adding said predomi- A contained therein,` settling.causing a predominantly aqueous phase to separate from a pre'- dominantly oil phase and adding the said predominantly aqueous phase to the said predominantlyl sludge phase to'eiect hydrolysis thereof.`

settling to form separable phases of which one is predominantly acid and recovering sulphuric acid 'Y from the predominantly acid phase. i L

6. An improved process according to claim 5' in -which the sludge material is obtained from the treatment with concentrated sulphuric acid of a'` petroleum residuum oil while dissolved in liqueiied propane. f

'1.l An improved process according toclaim' 5 in which the vpetroleum oil having a tween 25'and 55 API is kerosene.

8. An'improved process according to claim 5 in which the treating of the .predominantlyvbil between about .170 I.`

gravityvof be- 

